Spark plug



July 22, 1952 D. W. GREGORY ETALA SPARK PLUG Filed Sept. 22, 1948INVENTORS yles M Greyafy l (d i?. aldaffare i Y wh/wm Y ATTORNEYSPatented July 22', 1952 `ADouglas'fW. Gregory, Vergennes, Vt., aand;Egidiol R. Balda'ss'are, New VYork, N. Y.,-'-.assignors to `*SimmondsAerocessories, Inc., Tarrytown, NSY., a corporation of New York'Application SeptemberfZZ,

(Cl. 12s-169) 5 Claims.

Thislf'invention?relates to" imp'r'ovementsr in a' method-Lof:makingrspark plugs and` in. the" spark plugsfinad'e l thereby; f. -In a' moreparticular sense the invention `relates .aymethod of bonding metals withceramics; for 'example 1a metal elec- 5 trodetoan insulatorto form l1aVgastight yseal -be` tween'fthetwo. y

Various methods have beenemployed for the sealing lof electrodes Y inspark plugror igniter vin` sulatorsf" One successful' methodcomprisesa'seal formedfbymeltingifg-lass c'ontainingvrgraphite or metalpowder inside'the ceramic insulator and the' ceramic/and?` th'elmetallic electrodev contained.v thereinin accordancelwith- U. Se Patent2,106,578. In contradistinction;processes-have:been devel- 15opedffor'thel formingmi spark'plug center'v electrodes :bymeans offeasting: metal in the 'insulator borel toii'make permanent" and -xingengagement l withfa'fsparkingltip located' in theinsulator bore atitsrspar'kingend-in accordance WithSU. S. Pat` ent 2;*162,'062, theadvantage'thusgainedbeing the formation of." iin/electrical: conductorhaving form, f position)4r and'iproperties which' make for the`increasedponductionzof heat fromy said sparking-tip and,lessicertainly,lircmfthe insulatorY nose,` while mechanically ."'flxingand'at thel same 4time ntegrally unitingthefparts ini the insulator.'

Sparkfplugsfmadeiusing ithis latter4 process 'aswell lastl'ioseiproduoedaccording Ito thefdesigns'- and proce'ssesisetforth iii-British`vPatents 533,759,A 547,119; 559,805?andl56.?,064 fhave been found t0ShowfgaS-leakageasin' the usual method of presl` sure .testing sparkplugs.: vrFoi-.such reason it hasA beenrnecessaryfto use additionalsealing frneans' y suchirasy represented byth'e above citedU. S.' Pat-`ent 2;l06,578' invaddition to the subject vcasting process :1in l.orderto insure Vgas-tightness consid'- ered .essentialtov consistentperformance in`r spark plug operation.

Plugs :made/by castingor h'ot formingsilver in the insulator Jhavebeen`examined-in detail by breaking:thefzinsulatorfand exposing the castmetal core conductor. It was 'found' that vthe cast metalficoreWas-smooth and `that; itvdid not adheretothe-Wall of the insulator. Theinsulator had apparently/served merely as a'mold for castingoriormingthefsilver.' f n Accordinglrto the' present invention a method'has beenfdiscovered vbywhich ya cast metal is against thepassageof gasthrough threfinsulafA tor bore and toA enhance the .interchange of heatbetween the-*metalr and ceramicy insulator components.

The primaryf'object of the "invention is-,-there- .l l fore, tok providefanA improved'. method ffor :bonding c a metal tconductor' tof theinside wall ofv a; spark i pluginsulator;

prevent c gasA leakage; n

Another object of theinventionis tos-.provide an improved 'method *offbuilding-r af metal v`toa ceramic material.

Another object of 5 they inventionfis;l to. provide f an improved tspark-1 plug f in which i the electrode i conductor' is bondedto theinside Wall ofthe spark plug insulator.

Accordingto` apreferred'form of y the invention i t the improved sparkplug is manufactured bythe steps of mounting-a mjetalsealing--conejorfspike 1 in the lowerportion oinafsparkpluginsulatongthe cone being electrically connected toa-sparking'` 'tipextending from the tip of the insualtor pro- Y viding abody ofmoltenymetal*havingfafmelting point of approximatelythat ofsilVer-aroundVthe cone and to a' considerable vdepth in theinsulator,V inserting a.second ,metal'fsealing';y cone 1or spikeV pointed downwardlyA intheinsulator; abQveithe body of molten metal," and `applying pressure'to'the secondy cone to Ydrive it into andvtoapply pres.;y

sure to the moltenm'etalinltheiinsulator, whereby: o the moltenf metalis driven-suddenly into intimate" contact with the, hot inside-Walliolthe -`insulator f and bonded thereto.`

In afspe'cicform-'of theinventionxtheisealing coneused'in theybottom of:the-insulatorflist'pref y eraloly of*nickeLp-whilethesecond coneisprefer ably` of steel' 'and nickel;` and silver :plated:'with1` thesilversubsequently brazed'asiin hydrogen.l

In the drawings: l

Fig. 1 is avertical' or'longitudinalfview of a'24 f spark' plug'f'insulator ofA Iconvention'alf construe-i tion showin-g` therelationship of the 'parts'z inf the 1 l initial stageiof the procesa?4Fig. 215s view'simuar'tolthat fFigf. V1j show# ing the' relationshipkofthe parts' after fthe silver? orl othe'rfmtar has been -fmeited iii-thinsulation Fig. 3 is a longitudinal sectional view showing therelationship of the parts at the conclusion of the process.

Figs. 4, 5, 6 and 7 show modified forms of upper sealing cones or spikeswhich may be used in carrying out the improved process;

Figs. 8 and 9 show modified forms of lower sealing cones or spikes.Referring to Figs. 1 to 3 inclusive, of the drawings, the improved sparkplug of the present invention is made by providing a spark pluginsulator ID of conventional design and made, for example, by sinteringaluminum oxide or other suitable ceramic. This insulator, preferably ofan aluminum oxide type, has an upper relatively long bore I2 of largediameter, a lower relatively long bore I4 of substantially smallerdiameter, and a tip bore I6 substantially smaller than the bore I4 andpreferably of the correct size to t a sparking tip such as themetal tipI8, or an extension of a cone 20, to which a relatively shorter sparkingtip may be appended. The rst step in the process is to provide a lowersealing cone or spike such as the spike 2U which is preferably ofnickel, and which is also large enough or may be mechanically up-set orotherwise processed to preclude its complete passageoutwardly throughbore I6. The lower sealing cone or spike 20 may be provided with anextension of suitably small diameter to project through bore I`6whereafter it may attach to the sparking tip I8 of relatively shortlength. In the form shown in Fig. 1, lower cone 20 is welded to thesparking tip I8, the welding joint being shown at 22, and as providing arim resting in the lower portion of the bore I4. It is not necessarythat the cone or spike 20 be of larger diameter than that of thesparking tip IB, but it preferably extends substantially into the boreI4. After the cone 20 is in place a section of a silver wire 24 is setin the insulator on the cone so that when it melts it will somewhat morethan fill the bore I4. Instead of using silver wire powdered silver orother form of silver or a silver alloy may be used. Copper may also beused.

The insulator I6 with the elements shown in Fig. 1 is set in uprightposition in a suitable furnace in which the insulator is heated to atemperature above 1760 F., which is sufcient to melt the silver andcause it to run down in the bore I4 and surround the cone 20 in themanner shown in Fig. 2 of the drawings. If the cone 20 is welded orotherwise attached to the sparking tip I8 prior to starting the process,the arrangement is preferably such that none of the silver comes incontact with the tip I8 which is preferably of platinum or a platinumalloy of tungsten. The insulator containing the molten silver is removedfrom the furnace to a specially arranged press, after which an uppersealing cone or spike member 26 is quickly inserted into the insulatorand plunged or driven into the molten metal by applying a tool underpressure to the upper part of the cone. The cone 26, as shown in Fig. 2,includes a pointed spike section 28 and an upper open top shell section3U into which the tool for applying the pressure may be inserted. Theentire cone 26 may be of Bessemer steel such, for example, as screwstock and silver plated.

The pressure applied to the cone 26 should be somewhat of the order of4,000 pounds per square inch and applied quickly but over a period of afew seconds rather than instantly. W'hen the cone quickly chills thesilver and at the sam time forces the melted silver against the hot wallof the insulator I0. The shape of the cone 26 furthermore causes thechilling of the silver from the inside out. When the silver 32 hasfrozen it forms an intimate contact with the lower cone 20, with theupper cone 26 and with the contiguous insulator Wall, especially in theareas adjacent to members 20 and 26.

Fig. 3 shows a vertical section through the insulator after theforegoing operations have been completed and it will be noted that thesilver I2 is thoroughly bonded to the inside wall of the insulator I0and that the lower cone 20 extends into the body of silver while thesparking tip I6 has not been contacted by the molten silver in thecasting operation. The upper part of the body of silver 32 completelysurrounds the lower portion of the cone 26, the tip of which is somewhatdeformed to provide a sort of lock or enlarged portion around and overwhich the cast The upper cup-shaped or hollow section lll-ot l the cone26 is one convenient form of cone from i.

the standpoint of applying pressure in the operation and also from thestandpoint of using the cup to receive a resistor or a terminalconnector such as might be required in spark plug design.

The invention is not restricted to the useof a particular form of uppersealing cone shown in Fig. 2 of the drawings, but one of the forms shownin Figs. 4 to '7 inclusive, may be used. In Fig. 4 the cone 34 includesthe upper hollow section similar to lthat of cone 26 and an anchorsection 36 which is adapted to be driven into the molten metal in theinsulator so that the metal will solidify above the section 36 andanchorl the cone therein. The form shown in Fig. .5 is somewhat similarto that shown in Fig. 4. but is provided with a button type anchormember 38 Whiehjs adapted to be embedded into the molten silver underpressure, and which transmits a greater portion of the driving forcedownwardly through the silver column beneath it.

The cone structure shown in Fig. 6 includes a body 40 provided with theupper cup-shaped section and with a low melting point anchor member 42keyed to the body 4u but provided with an end section adapted to beembedded in the molten silver and to be melted thereby. The melting ofthe end section of the member 42 provides an intimate fused bond foranchoring thev cone in the silver body.

The sealing cone shown in Fig. 7 includes a pointed spike section 43similar to the spike 26 of the cone 25, an intermediate enlarged section44 of slightly larger diameter than the bore I2 of the insulator. Thissealing cone also includes an upper pointed section 45 of about the samediameter as the spike section 43.

molten silver in a manner similar to that of the sealing cone 26, thedriving member extending around the upper section 45 and vbearing on theshoulder of the section 44. The entire sealing cone is of solid metaland functions in much the same manner as the sealing cone or spikemember 26. After the sealing cone is drivenV into the l molten silverand the spark plug assembled. the

The sealingl cone shown in Fig. 7 is driven into the body of asomo??iipperJsection-il- 'serves to. .engage .the conductor or dampingmaterial in the:bore .I 2 in accordance-.z

with the usual practice.y v`The conesf. shownvin Figs.l 4zto -.7r are iadvantageously made of Bessemer..

steelscrew.` stock` and silver plated.

Fig. 8 of the drawings illustrates a modified'V tormbr'lowerfsealingcone construction comprising apointed upper portion lli-.of somewhatlarger; diameter than the .bore I6; the section. being; beveled@ downter a, smaller` cylindrical section 48Sy adapted;v to.. t .the bore I6.and extendf therethrough.; f The. lower. .end fof the cylindrical.section -48 is iwelded. or: brazed .to al sparking .tip550 fwhich.is..preferably of platinum or ansalloy; as referred to.; This tipmaybe convenientlyiwelded'- to theectioni.afterthe-upper coneisinstalled..

'I'heA insulator Inf shown; in. Fig.. 8l may have: a

countersunk portion .52 at; the lower.. end;` of the-1 bore- 'l 6 :sothat -theweld v'between the tipfand the section. 4B; is upfj within thiscountersunk portion,pas.;indicated. The section .48..will thereforebegsomewhatshielded from high temperaturesgandspark conditions existinginthepcyl-4 index' of fthe internal combustion engine in which...

the spark` plug -is used.

Fig.L v9; showsa modified form `of lower sealing coneior spike made ofthe same materials as' that-Shownin Fig. 1, and comprising a sparkingtip 54 Vwelded to aqspike orcone 55 by` an extending rim-,likaweldingjointv 58 having thev same function :as the vwelding joint 22 inFig. 1.The spike-.56 isof somewhat larger diameter than the tip Bland isprovided with aplurality of super- '1 or moresuch'actions, but-that hasnot beende-` posed, annular grooves 69 `of the shape shown..

One. ormore grooves llmay be used, which areadapted .tor receive moltensilver when the pressureisapplied, as-described above.y The sealingconeshown in Fig. Qtherefore provides a structure, Iaftercasting of thesilver, in which vone or moreannular flanges of, silver in the groove orgroovesy (iIJposi-tively` retain ythespike or cone in thesilvercastingand aid `in forming a .tight immovable connection adaptedto facilitate heat y sultisjshown in Fig. 3. Furthermore, sparkpluggunlts made in accordanceV withthe process K of thefpresentinvention havefalso been broken up aroundthe.silver-casting toinvestigate they bondbetween the body of silver and the wall of theinsulator l0.

In breaking up the lower portion of the insulator it was foundvthat -ithad to bebroken into relatively small pieces in order to. remove most ofit fromfithe body of silver 32; kEventhen,` iny a: larga-majority ofcases, the bodyof silver .was

substantiallyy completely -coveredY `with the material of the insulatorin chips and layers, showing that the bond between the silver and theinsulator was stronger than the internal bond of the insulator. In manycases where attempts were made to break the insulator away from the bodyof cast silver it was found that a considerable number of pieces of theinsulator would adhere tenaciously to the body of silver and thatfurther breaking of these pieces would still leave an irregular coatingof the insulator material on the silver all along the casting.

Not all, but a large majority of the insulators,

brokenfupto determine the adherencenoi!the.VA f silvertothe-insulator.:show a uniform bond bes; f tween-the silver and theceramic insulator.'However; iny all cases there was' denite bonding fbcf tweenthe silver`and the insulator, and4 all vunits@v f werefleak-.prooh asdistinguishedfrom spark plug.` units made by previously known-processes, such. asthose yrefer-red to above. Spark plugs made by. f previously knownsilver casting methods were lll'A side-of lthewsilver castwas smoothandvnot bonded broken-and examinedto -lnd only that the :out-

to the insulator.

The-phenomenon involved in the bonding of f the silver-y to4 the ceramicinsulator without the use oany bonding agent`y is not fully understood;but, irriportant-asarel the pressure vrelationships-v of the' process,investigation has shownv thatnickel, such as the nickel cone.-20 or 56,facilitates l bonding. There may be some complicated physical, chemicalor catalyticaction involved, or two termined; It does appear frominvestigation, however, that thecarrying out of-the process in anatmosphere of hydrogen adversely afectsf the bonding.

It also appea-rsnot'agltogether desirable to make cone v2ll1ofa materialwhich -will readily form" a fusionI bond `withthe silver-'or of heatconducting This ispossiblyone of4 thek'eys to theA success Lof-ftheprocess-for reasons whichmay be explainedaasvfollows: In aninsulator-whichisA cooling after processing' as Yldescribed'f* the-bondbetweenv the ceramic and" the silver' isy greater metal.

thanl that ybetween the silver and the nickel-of cone,y 20.

may occur without opening -up any leakage paths.

In order fto oit-set `possible maladjustment of thev heatowffpatternasaectingfheat picked up Vby the sparking tip, coney 20-v may/.be madeAto `con-y taingrooves v asf shown in Fig. 9,- such that willinsure.;intimate-@mechanical pressure exerted vbe tweerrsueh. groovesduringT the contraction phase of thegprocessl Heat flow` at the cone to'silver interfacermayalso beinsured by the .employment of plated orbrazedgcoatings whichcoveronly-a portion of. the sealing.` cone orwelded extensions.

of a -metal yor metals. which. enterv into. fusion bondinggwith .the.molten silver.

The .1 unusual: results obtained. with'i sparkzplug.. i

units,mayin. some respectsbe due to .the posi;- tions and manner ofusing the spaced upper and lower cones,A or to these factors incombination. withtheuseof nickel and presence orair. When the upper'.cone is plungedinto the molten silver under..pressure,the:fupper,andlower cone `tips appear.v to'. act as. plungers Yand-force .the molten fsilver`r toward ,the-hot lwall. ofV theinsulator l0.; At the-.same timethe .coolingis most rapidiat, thetopgand bottomfandy vfrom theinsideyofthe I body.. inview of the.cold upperconeand the. conduction ofyheat from the "cone .20 .to .the tip..

Stresses set up in this region as a result of the differences between`the-contractionrates Aof the silverand ceramic-are thus relieved v atthe silver-nickel linterface-where break-'downy a sealing or' bondingmaterial has been found*l to give certain advantages over othermetalsbecause it can be heated and processed in the open atmosphere without aspecial type of furnace to prevent oxidation. Other metals or alloysmelting in the neighborhood of the melting point of silver may be used,for example, copper or a metal powder mixture consisting of 80% silver,9% iron, 9% nickel, 1% carbon and 1% flux such as borax. Other silveralloys may be used, as for example, sterling silver or an alloycontaining from 1% to 5% of nickel.

According to the preferred form oi the invention, the lower sealing coneis made of pure nickel or steel plated with nickel, while the uppersealing cone is of steel plated successively with nickel and then withsilver, the latter of which is subsequently hydrogen brazed` to thenickel undercoating. In some cases a copper undercoating may be used inplace of nickel.

The process may be employed for the bonding of metals to ceramicmaterials and to glass for various purposes. Many insulatingrnaterialsare glass or contain glass.

What is claimed as new is:

1. A spark plug including a central insulator having a sparking tip ofcorrosion-resisting metal projecting from its lower end, a metal sealingmember comprised of nickel connected to said tip and extending into saidinsulator, a body of cast metal containing silver surrounding saidmember and intimately bonded to the inside wall of the insulator bydirect contact of the cast metal with the insulator wall, and an uppersealing member anchored in said cast metal body by means of a projectionextending into the body and partially enclosed thereby, the upperportion of the upper sealing member substantially fitting the bore ofthe insulator.

2. A spark plug insulator construction ccmprising a ceramic body havinga longitudinal bore and a tip portion from which a metal sparking tip ofcorrosion-resisting metal extends, a cast metal body in the insulatorbore in the portion adjacent said sparking tip, a nickel spikeelectrically connected to said tip and embedded in said metal body, anda second metal member having an elongated pressure-exerting and pointedanchoring portion extending into the opposite end of said metal body andanchored therein, the cast metal body and the wall of the insulatorbeing bonded together by a bond adapted to join and seal the metal bodywith respect to the insulator.

3. A spark plug insulator construction comprising an elongated ceramicinsulator having a longitudinal bore, a nickel connector and sealin-gmember located at its operating end and extending into the insulatorbore as well as extending outwardly from the operating end of theinsulator, a metal sparking tip of corrosion and erosion resisting metalsecured to the outwardly-extending end of said member, and a cast metalbody in the bore in contact with and sur-- body being bonded directly tothe inside wallof f the insulator bore with a. strong intimate bondadapted to provide an effective seal against the leakage of gas betweenthe metal body and the i insulator.

4. A spark plug including a central ceramic insulator having an axialbore, a sparking tip of corrosion resisting metal projecting from thelower end of the insulator, a metal sealing member connected to said tipand extending into thev bore of said insulator, a body of cast metalcon-y taining silver surrounding said member and in' 1 timately bondedto the inside wall of the insulator by direct contact of the cast metalwith the nsulator wall, andan upper metal sealing mem- 'ber platedsuccessively with nickel and silverl said upper. sealing member beinganchored in said cast metal body by means of a projection extending intothe body and partially enclosed thereby,

the upper portion of said upper sealing member substantially fitting thebore of the insulator.

5. A spark plug insulator construction comprising an elongated ceramicinsulator having a longitudinal bore, a metal sealing-member extendingfrom the bore at the operating end of the insulator and also extendinginto the bore and terminating therein with a pointed end as a sealingmeans, a cast metal body in the insulatorV bore surrounding and bondedto the portion of the metal sealing member in the bore, said cast metalbody extending in the bore beyond said f pointed end, and a metal memberhaving an elongated pressure-exerting pointed anchoring portionextending into the cast metal body at its end remote from the operatingend of the insulator and anchored in and bonded to the cast metal bodyin spaced relation to said pointed end,

said cast metal body being bonded directly tov the inside wall of theinsulator bore with a strong intimate bond adapted to provide aneffective seal against the leakage of gases between the cast metal bodyand the insulator.

DOUGLAS W. GREGORY. EGDIO R. BALDASSARE.

REFERENCES CITED The following references are of record in the le orthis patent:

UNITED STATES PATENTS

